dussaussoy etal



June 26, 1956 P. DussAUssoY ErAL 2,752,532

MANUFACTURE PROCESS OF TUBES OR VACUUM ENVELOPES Filed Jan. 17, 1951 2Sheets-Sheet 1 l/V VE/VTORS June 26, 1956 P. DUssAussoY ETAL 2,752,532

MANUFACTURE PROCESS oF TUBES 0R VACUUM ENvELoPEs Filed Jan. 17, 1951 2sheets-sheet 2 /IV V/VTORS ,1D/@w25 .ox/SSA asso y, MA x/ME 6R V07',

l ArroR/VEY MANUFACTURE PROCESS F TUBES OR VACUUM ENVELOPES PierreDussaussay and Maxime Grivot, Paris, France, assrgnors to CompagnieGenerale de Telegraphie Sans Fii, a corporation of France Application.l'anuary 17, 1951, Serial No. 206,347

lairns priority, application France March 4, 1950 8 Claims. (Cl. S16-19)The invention relates to tight and permanent joints, and moreparticularly to vacuum tight joints designed for the manufacture ofhermetically closed envelopes and especially those of radio andtelevision tubes, gas tubes and similar devices. It aims moreparticularly at joints between parts placed end to end, of the same orof different materials, but offering practically the same coefficient ofexpansion.

The technical progress in radio-electricity, involving the use of higherand higher frequencies, imposes on the manufacturers of electronic tubesvery strict conditions of geometric precision in the assembling of theelectrodes, the position of which should be all the more rigorouslydetermined and maintained as the lengths of the wave decrease.

On the other hand, the use of very high frequencies imposing specialconduction conditions, often makes necessary the use of metals which arevery good conductors in the making of the tight envelope. This casearises particularly when the envelope forms part of a resonator.

The conventional method which consisted of melting the end of one of theparts in order to solder it to the other part of the envelope, can nolonger satisfy these conditions for the relatively high meltingtemperature of the metal causes a dangerous alteration of theelectrodes, or else reacts on their positioning. Since the heatingoperation was made when the cathode was in an enclosure still lled withair, the oxidation of said cathode was always detrimental, and it causedlarge losses. Besides, the fact itself of using the ends of the parts ofthe envelope involved relative displacements of the electrodes supportedby these parts, and changed their geometry.

If, in order to reduce the temperature, one resorted to the contrivanceof an enamel rim between the parts to be hermetically united, onenevertheless always had to effect the fusion of this rim, introducing acollapse of the parts and a disturbance of the spacings of theelectrodes, and subjecting, on the other hand, the cathode in the air tothe danger of oxidation.

The present invention has as its object a new method for making stableand vacuum-tight joints, no longer having the above-mentioned defectsand permitting of manufacturing the tubes with a minimum waste, andoffering all the guarantees of positioning and quality of theelectrodes. l

The invention is directed to an industrial method permitting the tightjoining of parts made of materials with very high melting points, andparticularly ceramic parts either among themselves, or with parts madeof metals which are good conductors.

Furthermore, the invention permits of Sealing the glass parts withouttheir edges being subjected to `a temperature causing their deformation;and in a general way, the invention permits of joining parts of whatevernature, without attaining the state of softening.

The invention also permits of maintaining a high vacuum inside of theenclosure during the thermic phase,

nited States Patent lice and of thus preventing any oxidation oralteration of the electrodes.

The invention permits of industrially making electronic or similar tubesfor very short waves, of a very reduced size, satisfying all therequired conditions.

Finally, the invention permits of effecting tubes made entirely orpartially of ceramics or of glass, in which the tight joints serve aslead-in current conductors.

According to the invention, the surfaces of the parts designed to beplaced in contact, after having undergone a suitable machining, arecoated with a thin layer of silver closely adhering to the support andin tight contact with it. This silver coating is then polished ascarefully as possible, preferably to an optical polish. The parts arethen applied one against the other so as to form the closed vessel whichis then subjected to the pumping operation until a high vacuum isobtained. The tightness while cold already secured from the contactbetween the optically polished coatings, concurrently with the effect ofouter pressure owing to the vacuum, makes this operation possible. Thecompletely emptied tube is then subjected to a heat treatment having theeffect of bringing the joint between the silver coatings to atemperature which transforms it into a permanent seal, free from oxides,by molecular diffusion between the two parts under the combined effectof the heating and the pressure. This operation is assured by anysuitable means, and preferably inside the degassing oven; and thethermic application is controlled so that the support-parts do not reachthe state of softening. The cold-tight opticallypolished contact is thustransformed into a permanent joint, without the intermediary silverlayer, nor its supports, undergoing a softening effect, and thus withoutrisk of deformation by the action of the external pressure.

The use of silver films is particularly advantageous in all cases inwhich the parts of the joint are made of materials which do not diffuseone into the other by molecular diffusion, or do so at too hightemperatures, at the risk of causing the softening, and thus prohibitivedeformations of these parts. In certain cases, especially when one hasto do with parts in which the silver can diffuse directly at atemperature lower than that of the softening of the parts, oneV coulduse, without thereby departing fromthe scope of the invention, a singlesilver film, covering only one of the parts, the other remaining bareand receiving of course, the appropriate polishing. The moleculardiffusion will thus be produced between the layer of silver and thepolished surface of the bare part. In general, this layer of silver willbe placed on the part offering the least affinity for moleculardiffusion, and particularly on the ceramic part in case of aceramicmetal joint, or on the metal in case of a metal-glass joint, etc.

For the silver, any other substance may be substituted, preferablynon-oxidizing, which satisfies the conditions of close adhesion to thesupport, forming a tight and continuous film and lending itself to anoptical polishing and to molecular diffusion at relatively lowtemperatures, and particularly that of the degassing, lower than thosecausing the state of softening of the component parts.

Instead of placing the parts end to end and reconciling; their expansioncoefficients, one could, according to one variant of the invention, alsogive them a concentric arrangement and thus be able to use parts havingdifferent coefficients and working at radial compression.

For the silver one could substitute gold or platinum, both of thesemetals perfectly satisfying tne above-stated characteristics, andfurthermore lending themselves to a molecular diffusion which assuresthe joint, at temperatures very much below those of their softening, andconsequently lending themselves to a heat treatment transforming thetight contact into a seal not necessitating an exact control of theheating Vmeans, which is Aof particular interest in the use of ovens forthis purpose.

According to one variant of the invention, the surfaces designed to comeinto contact, after having been carefully prepared so as to conform oradjust perfectly to one another, are cleaned and receive the silver bypainting, in the colloid form mixed with a small amount of enamel powderserving as a glue; this deposit is then subjected to a suitable heattreatment process.

According to another variant of the invention, thc metallic coatingcould be effected by electrolytic deposit, indicated especially when itis a question of metallic supports.

lt is very useful, for the polishing, to anneal the glass parts in orderto annul the internal tensions which exist in the glass, and which may,at the moment of heat treatment designed for the sealing, causedetachments between the parts, thus compromising the tightness of thejoint. This annealed effect is often obtained before by the baking ofthe silver-enamel layer, described above, if the temperature of thisbaking, as well as its length, correspend to the annealing conditionsfor the glass in question.

The envelope effected according to the invention will be characterizedby the presence of a thin layer of silver or of another equivalentmetal, extending over the whole section of the joint, between thedifferent parts and more particularly in contact with its ceramic orglass parts.

The opposite optically polished surfaces being in general more extendedthan the seal proper limited to the intimate contact, the envelope willoffer in addition the characteristic particularity of the presence of aglittering surface in the vicinity of the seal, owing to the fact thatthe heat treatment regulated well below the softening temperature, hasnot altered the state of this surface.

lf the silvered surface exceeds the joint proper, outside of theenclosure, it will in time lose its glittering appearance because of theoxidation of the silver, but will nevertheless retain its polishedappearance.

The finished envelope will be also characterized by the fact that theedges of the parts in tight contact, and more especially of the glassparts, have kept their initial shape, the heat treatment not having madethem pass into the viscous state; in particular they retain their sharpedges due to their surfacing. These parts also retain the sharp andweil-pronounced angles between their edges.

The tube made according to the invention can have terminals orequivalent external means of connection, joined to the silver layer ofYthe joint, between the parts made of insulating substance.

An oscillograph tube made according to the invention will have aterminal glass plate supporting the fluorescent screen, sealed by thesilver hlm to the body of the envelope, and this film will be extendedonto the outer wall in such a way as to engage there the currentContact, as on thc inner part, so as to join this contact to theconducting coating inside of the tube.

Other modes of manufacture and assembling electron discharge tubes willbe described in detail in the text which follows.

By way of non-limiting examples, and in order to illustrate the numerouspossible applications of the method according to the invention, therehave been shown on the accompanying drawings several embodiments ortypes of vacuum enclosures made according to this method.

Figure l is a vertical sectional view of a sealed disk triode of theso-called light-house-tube type, the walls having parts ot glass andparts of metal; Fig. 2 is an enlarged fragmentary portion of thestructure; Fig. 3 is a vertical sectional view showing the applicationof the invention to a tube structure where the walls are formed fromceramic material; Fig. 4 shows in longitudinal section atelevision-oscillograph cathode ray tube made according to conventionalmethods; Fig. 5 isla longitudinal sectional view of a televisionoscillograph-cathode ray tube manufactured according to the method ofthis invention; Fig. 6 shows the application of the method of theinvention to the manufacture of a conventional electron discharge tube;and Fig. 7 is a vertical sectional view showing the assembly, accordingto the invention, of an exterior anode type of tube.

In the example of the invention as applied to a lighthouse-tube such asthat shown in Fig. l, the method of the invention permits of obtaining agreat precision, because of the fact that the seals are made metal onmetal, without the interposition of oxides. The dilerent elements ofthis tube are: a base of pressed glass A, bearing the cathode block G; acupel B in metal welded to the glass, for example in dilver p copperedor silvered (dilver being an alloy, corresponding to Kovar, of iron,nickel and cobalt); a glass ring C; a metallic disk grid support D;another glass ring E; finally, an anode-holder part F, for example ofthe same metal as the part B.

The edges of all these parts, in 1, 2, 3, 4, 5, 6, 7, 8, 9, and 1t) areperfectly dressed by line emery wear on a metallic plane; a subsequentcleaning removes all trace of abrasive and grease from these surfaces,which are then covered by brush with a tine layer of metal in thecolloid state, for example colloid silver containing a very smallproportion of powdered enamel. This done, the different parts are tiredin the furnace at a temperature generally between 450 degrees and 750degrees C., for a suitable time, variable, moreover, with the bakingtemperature. A final surfacing, consisting of friction on a clothpolisher smeared with polishing paste permits of reaching a degree ofpolishing suitable for the layers of colloid metal.

It sutiices therefore, to align the diierent elements thus prepared oneagainst the other in complementary relation, to make the vacuum in theenclosure formed by this juxtaposition (the external atmosphericpressure sutlicing to maintain the various parts firmly applied the onesagainst the others), and finally, to bake the whole at about 450-500degrees C. for at least an hour. After cooling, an extremely strongenclosure is obtained, comprising live perfectly tight sealings.

The sealing operation is more clearly disclosed in Fig. 2, showing on avery much enlarged scale, the joint between the parts A in glass and Bin metal of Fig. 1. 1B and 1A represent in Fig. 2 the thin layers ofsilver adhering solidly and tightly to the surface of these oppositeparts and forming there a continuous lm. Their thickness will vary forexample between 0.2 and 3 hundredths of m./m. depending on the number oflayers applied. These layers are optically polished and their closecontact keeps the vacuum. The envelope can be exhausted to a highvacuum. subjected to heating inside of an oven, this contact istransformed into a seal by the phenomenon of molecular migration betweenthe two films, when the temperature has reached to around 450 degrees C.During this transformation the joint is subjected to the outeratmospheric pressure, and it completely retains its solid structurewithout reaching the viscous state, and consequently continues tosupport the vacuum.

This relatively low temperature of molecular diffusion assures arelatively large margin of safety before reaching the point of softeningof the glass, which is located at around 530 degrees C., which is veryadvantageous in the case of glassrparts; and this temperature is thus a'good deal lower than that of metal deformation, which is practicallythe same as its melting point and is located for silver, at around 950degrees C. Thus one runs no risk of softening the parts in contact andone is completely able to assure this heat operation in the oven whichserves for the degassing, and to combine it with the degassing operationwithout being obliged to carefully regulate the temperature of the oven.

It is to be noted that the fraction PO inside the space of the surfaceof the layer 1A, which extends beyond the joint proper at the interiorof which the two lms are closely bound together by forming a homogeneouslayer. The interior extension of the joint will retain itsopticallypolished appearance. In fact, since the seal is produced at atemperature considerably below than that of melting for silver, itssurface will not undergo any alteration and will keep the glitteringappearance.

The glass part A as well as the metal part B, not having been subjectedto the deformation temperature, Will completely retain their initialshape and will in particular retain the sharp angle tp caused by theinitial machining; and the silver film will also retain its mechanicalresistance. The geometry of the tube will undergo no alteration in thecourse of the sealing.

Since the heating operation is made while the electrodes are in the highvacuum, no alteration, and particularly not their oxidation occurs.

No oxidation is to be feared either, of the internal walls of themetallic parts of the envelope of oxidizable metals, such as copper.This is especially advantageous in electron discharge tubes designed forcentimetrical waves and of which the metallic walls form part oftheresonant cavities. Even a supercial oxidation introduces losses in suchtubes which compromise the operation, because of the pellicular effectof the conduction. For its part, the silver joint not being subject anytrace of oxidation, does not risk offering a resistance to the surfacecurrents.

Instead of giving a plane shape to the contact surfaces, in numerouscases, in order to facilitate the manufacture, they will be given aslight curvature. The surface of one of these parts will be convex, thesurface of the other will offer a complementary concave profile takingon exactly the profile of the first part. These profiles are obtained byfriction (as well during the griding operation as during the polishing)against a suitable body of spherical shape. This latter will in mostcases be driven by a rotary movement.

in the example of manufacturing the vacuum tube shown in Fig. 3 thedifferent elements of the wall are described successively as abase-cupel H in tight ceramic, bearing the cathode block G; a cupel Iand a disk I also of tight ceramic; and finally a cupel of tight ceramicK bearing the anode L of dilver p. The edges of these parts, 11, 12, 13,14, and 16 are silvered according to the process described above; on theother hand, the cupel I as well as the disk l' are silvered on part oftheir surface to serve as current lead-in conductors, appearing forexample, in the form of coaxial conductors; finally the traversingconductors M from the cathode block G are metallic, whereas the exhausttube N is of glass. The assembling of the tube is accomplished as in thecase of Fig. l.

The method of the invention finds a particularly interesting applicationin the construction of television cathode oscillographs, the making ofwhich is quite delicate, especially when the tube is to have a largediameter.

In these tubes, in fact, of which Fig. 4 shows one section, it isnecessary to have a post-accelerating electrode generally made up of acolloid graphite layer O placed on the inner wall of the enlarged partof the tube, this layer being brought to the high tension potential bythe intermediary of a metallic traversing conductor P.

in the example of manufacture according to the method of the inventionof an oscillograph tube, shown in Fig. 5, the end-plate Q serving asviewing screen is covered over on its periphery, at 17, with a thinlayer of polished silver; likewise, the edge of the bulb R at 18 iscovered with a similar layer of silver, a layer which extends onto apart of the wall, toward the inside at 19 and toward the outside at 2t);finally the colloid graphite O is deposited on the inner wall 21 andalso partially covers the silver layer 19.

After assembling the mirror Q and the bulb R, and then baking, a tightsealing without deformation is ob- Cil tained; the silver circumferenceof the end of the bulb, as all around the screen, constitutes anintegral part of the accelerating electrode and serves at the same timeas metallic traversing conductor for this electrode.

Furthermore, the luminescent layer deposited at 22 on the internalsurface of the mirror Q cannot be negatively charged, since it is joinedby the peripheral silver layer 17 to the post-accelerating anode itself.In addition, the mirror Q can be perfect, for it can be opticallysurfaced, which is not of negligible interest in projection tubes.

Fig. 6 deals with the manufacture of a conventional tube by the methodof this invention. The base S and the flask T are as hereinbefore,silver-plated on their 'edges at 23 and 24, edges which may be ofpolished spherical surfaces, which facilitates the obtaining of asuitable optical polish when it is a question of using flat pressedbases.

Finally, Fig. 7 shows the construction, by the method of the invention,of an external anode tube. The space of this tube is made upsuccessively of the anode U, which may be of copper, to which there willbe united a part U in the shape of a ring of dilver P metal brazed at uonto the body of the anode; by an insulating part V, of tight ceramic,profiled in such a fashion that it increases the lines of leakage; by ametal ring, W, of dilver p"; and finally by a base-cupel X of tightceramic supporting, with W, the grid and cathode G.

The edges of the different parts are rectified, silverplated, thenpolished, at 25, 26, 27, 7.8, 2S? and 3f), and then assembled and sealedas in the preceding forms of the invention.

While our invention has been described in certain preferred embodiments,it is realized that modifications may be made and no limitations uponour invention are intended other than may be imposed by the scope of theappended claims.

What we claim as new and desire to secure by Letters Patent of theUnited States is as follows:

1. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope in abutting relationship, consisting of machiningthe opposed edges of the coacting parts to give them complementarysurfaces enabling the parts to establish an accurate mating relation,coating at least one of the mating edges with a thin layer of asubstance which adheres intimately and tightly to the surface of thesaid edge, said coating having the property of molecular diffusion underpressure in the material of the edge of the opposite mating part at atemperature lower than the deformation temperature of said joined parts,imparting to said coating and to the edge of the opposite mating part apolish of the character required for a vacuum-tight contact-joint,creating a high vacuum within said parts when in assembled matingrelation with said polished edges in direct contact, and heating thezone of said contact while submitting the mating parts to pressure toseal the contacting intimately mating edges by the effect of theirmolecular diffusion in a solid state below the deformation temperatureof the parts.

2. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope, as set forth in claim l, in which said polishedcoating is formed from metal.

3. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope, as set forth in claim l, in which both envelopeparts to be joined are coated with a metal film adhering intimately andtightly to the envelope part, each film being polished, so as to form,when in mating contact, a high vacuum-tight joint.

4. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope, as set forth in claim 1, in which both envelopeparts to be joined are coated with a silver film adhering intimately andtightly to the envelope, each film being polished, so as to form, whenin mating contact, a high vacuum-tight joint.

5. A method of producing a vacuum tight sealed joint between parts of ahermetic envelope of an electron tube and similar device, consisting ofmachining the opposed edges of the envelope parts to give themcomplementary surfaces for establishing an accurate mating relationtherebetween, coating each of said edges with a metal lm adheringintimately to the parts and having the property of mutual moleculardiffusion in the solid state under pressure at the temperatures whichare substantially lower than the temperatures at which the joined partsundergo deformation, polishing said lms to an optical degree, assemblingsaid parts in mating relation to form a vacuum tight envelope, pumpingout the envelope to high vacuum and, while the parts are compressed bythe external air-pressure, submitting said envelope to degassingoperation, the temperature of which is regulated to seal the contactingpolished edges by the ettect of their molecular diffusion in a solidstate below the deformation temperature of the parts.

6. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope as set forth in claim 5, in which the metal filmwith which the parts are coated consists of a thin layer formed by amixture of colloidal silver and enamel in a paint-like state, andwherein the coated parts are initially heat treated by ring to form asolid coating prior to said polishing operation.

7. A method of producing a vacuum tight sealed joint between two partsof a hermetic envelope as set forth in claim 5, wherein at least one ofthe parts to be joined is of glass, and wherein the sealing of thehermetically mating optically polished metal coatings is secured bykeeping the degassing temperature below the deformation temperaturesrange of the glass and Within the difusion temperatures range of saidmetal coatings.

8. A method of producing vacuum tight envelopes for electron tubes andsimilar devices comprising at least one glass part, consisting ofmachining the opposed edges of the` envelopeA parts to be joined, togive them complementary shapesfor establishing an accurate matingrelation therebetween, coating each of said edges with a silver lmadhering intimately and tightly to the part, polishing said films to anoptical degree, assembling said parts in mating relation to form a tightenvelope with said silver film disposed between the parts, pumping outsaid envelope to high vacuum and, while the parts are compressed by theexternal air pressure, submitting said envelope to degassing operationand, during said operation, heating the contacting polished edges toseal them by the effect of their molecular diffusion, said heatingoperation being regulated to avoid the deformation of the envelope glassparts.

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